1. Field of the Invention
This invention relates to an outboard drive unit for a watercraft, and more particularly to a power tilt and trim system for an outboard drive unit.
2. Description of Related Art
Outboard motors with four stroke engines have grown in popularity in recent years, due in part to environmental concerns associated with two stroke outboard motors. The application of four-cycle engines in outboard motors, however, has raised some challenges, especially with large horsepower engines. A four-stroke engine will weigh significantly more than a two-stroke engine that produces a comparable horsepower to that of the four-stroke engine. The additional weight requires a hydraulic power tilt and trim system even for an outboard motor that employs a small horsepower engine.
The hydraulic power tilt and trim system supports an outboard motor on a watercraft and adjusts the trim and tilt position of a drive unit of the outboard motor. A tilt and trim adjustment mechanism of the system commonly includes at least one hydraulic actuator which operates between a clamping bracket and a swivel bracket. The clamping bracket is attached to the watercraft and the swivel bracket supports the drive unit. A pivot pin connects together the swivel and clamping brackets. The actuator causes the swivel bracket to pivot about the axis of the pivot pin, relative to the stationary clamping bracket, to raise or lower the drive unit. The actuator usually includes a closed cylinder and a piston slidably supported within the cylinder.
The actuator has two particular roles. One role is to adjust trim angles of the drive unit so as to adjust further positions of an associated watercraft. This trim adjustment can be done within a trim range in which the drive unit moves from a fully lowered down position to a certain raised up position, i.e., a fully trimmed up position. Another role of the actuator is to bring the drive unit out of the surrounding water halfway or completely and vice versa. This movement is done within a tilt range in which the drive unit moves to a fully trimmed up position, i.e., fully tilted down position to a fully tilted up position.
Tilt and trim adjustment mechanisms also usually employ a powering assembly that affects the trim and tilt operations of the drive unit. For this purpose, powering assemblies have included a reversible electric motor that selectively drives a reversible fluid pump. The pump pressurizes or depressurizes the actuator for raising or lowering the drive unit.
In particular, the fluid pump supplies pressurized fluid to various ports of the actuator's closed cylinder, on either side of a piston that slides within the cylinder. The piston forms separate chambers within the cylinder. A conventional seal, such as one or more O-rings, operates between the piston and cylinder bore to prevent flow between the chambers. The piston moves within the cylinder by pressurizing the chamber on one side of the piston and depressurizing the other chamber on the opposite side.
An actuator arm is attached to the piston and to the swivel bracket. The other end of the cylinder is attached to the clamping bracket. Alternatively, the actuator arm can be attached to the clamping bracket and the other end of the cylinder can be attached to the swivel bracket. By pressurizing and depressurizing the chambers within the actuator, the piston and thus the drive unit can be moved.
U.S. Pat. No. 5,049,099 illustrates a typical arrangement of the actuator and powering assembly. In this arrangement, a single actuator and a powering assembly are located adjacent to each other in a side-by-side relationship. The powering assembly formed by the pump, reservoir and motor extends along side the actuator for most of the actuator's length. Both the actuator and the powering unit lie between bracket arms of the clamping and swivel brackets. While these components are shielded in this position, the resulting assembly off sets the actuator from the center of gravity of the drive unit. That is, the stroke axis of the actuator and the center of gravity of the drive unit which it moves, are not within the same plane. Consequently more force is required to raise the drive unit, which increases the size of the actuator.
With large size outboard motors, this result was relatively acceptable. However, small size motors were forced to have other structures to accommodate the resulting larger sizes of the actuator, motor and pump. One approach for resolving the problem involves providing a completely separate power tilt and trim device and instructing a user of the motor to attach it to the outboard motor in his or her option. This approach requires too much work for the user. Thus, another solution is still sought.
In addition, preferably, the swivel and clamping brackets are reinforced to handle the increased weight. Even though additional reinforcing is difficult, the brackets should not lose their conventional sizes so as to preserve necessary strength. In particular, the bracket arms should keep sufficient lengths for securely supporting the drive unit on the associated watercraft.
Although the problems are notable with a small size outboard motor that employs a four-stroke engine, a large size motor that employs a four-stroke or two-stroke engine may have the same problems.
A need therefore exists for an improved construction of a power tilt and trim system that can support a drive unit in compact nature without significantly reducing construction strength.